This invention relates to the field of spiral-type hollow fiber membrane fabric-containing cartridges and modules for separations and other phase contact applications. In particular, this invention relates to improved cartridges and modules containing flow-directing baffles. The teachings of this invention can, if desired, be used in conjunction with the subject matter of applicant's copending U.S. patent application entitled, "Spiral-Wound Hollow Fiber Membrane Fabric Cartridges and Modules Having Integral Turbulence Promoters", filed concurrently herewith, which is hereby incorporated by reference.
There is a great deal of prior art relating to the structure, fabrication and use of spiral-type hollow fiber-containing cartridges. Among the early disclosures of such devices are Mahon U.S. Pat. No. 3,228,877 and McLain U.S. Pat. No. 3,422,008, both of which are incorporated herein by reference. In general, a bundle of hollow fibers is positioned around and parallel to the longitudinal axis of a rod-shaped core (which may be a hollow mandrel and may or may not be removed after the bundle is fabricated), the ends of the hollow fiber bundle are potted in tube sheets, and the cartridge is fitted into a pressure housing suitably ported to facilitate feed, permeate and concentrate flows, to constitute a complete module.
More recently, the art has improved such cartridges by forming the hollow fibers into a fabric-like web in which the hollow fibers, parallel to the core axis, are held in place relative to each other by transverse filaments which may or may not also be hollow fibers.
Despite these developments, the challenge to optimize the operability, efficiency and durability of these hollow fiber-containing cartridges has continued. The flow of fluids (both liquid and gaseous) through the bundle can present further problems for the operator, including channeling, growth of boundary layers and other inefficiencies in fluid/membrane contact (which may prevent effective mass transfer). Hence, some recent developments in the art suggest the addition of flow-controlling baffles.
The Caskey U.S. Pat. No. 4,929,259 discloses hollow fiber-containing spiral cartridges having baffles which are parallel to the core axis, intended to promote countercurrent flow. Either one spiral baffle wound up with the hollow fibers onto the core, or a series of concentric annular baffles enclosing the hollow fibers, may be employed. (See also, Caskey U.S. Pat. No. 4,961,760, and Trimmer U.S. Pat. No. 5,013,437).
The Neuhaus U.S. Pat. No. 4,649,991 discloses a hollow fiber cartridge made from stacked layers in which the hollow fibers are intermittently bonded by crosspieces which are superimposed to form flow channels for the hollow fibers in the cartridge. The crosspieces of each layer of hollow fibers are superimposed in a stack, so that they form a shell-side flow barrier when assembled.
The baffles taught by the Caskey patents run parallel to the core axis: they do nothing to address channeling and boundary layer growth, which both promote fluid flow tangentially along the longitudinal direction of the hollow fibers with inadequate contact on the membrane surface. The Neuhaus cartridge is not a spiral-type device, because the layers of hollow fibers are stacked, rather than rolled up. Moreover, since such cartridges are formed by a stacking procedure, they will be relatively square or rectangular in cross-section--not round. The resulting cartridge will contain "dead space" with uneven flow at the sharp corners, and construction of an appropriate pressure container to handle the high stresses in the centers of its flat sides will be relatively difficult and require added structural materials. Further, as illustrated in FIGS. 2 and 3 of Neuhaus, the crosspieces for each stack must be carefully lined up during manufacture--a difficult, tedious and inherently unreliable operation. Moreover, although the crosspieces promote transverse flow in the cartridge, such flow is not symmetrical with respect to the core axis, and is therefore not radial flow: this results in inefficient fluid-membrane contact.
It is therefore an object of this invention to provide improved spiral-type hollow fiber membrane fabric-containing cartridges and modules containing flow-directing baffles, for separations and other phase contact applications.
It is another object of this invention to provide such cartridges and modules in which flow-directing baffles are axially positioned to promote radial flow of fluids throughout the hollow fiber bundle.
It is yet another object of this invention to provide such cartridges and modules in which feed fluid flow is intermittently directed near to and/or through a portion of the core, and subsequently out to the periphery of the bundle.
It is still another object of this invention to provide a number of cartridge and module designs yielding radial feed fluid flow patterns which can be selected for particular desired membrane contact regimes.
It is an additional object of this invention to provide methods for constructing the improved cartridges.
Further objects will be set forth in the discussion below.